I hear this muddy defense of billionaires every time anyone tries to compare the wealth held by the working class vs. the ruling class, and it's pure BS.
A billionaire's net worth is measured in dollars. If that isn't a valid unit of measuringing their wealth, then find another way to measure it. The theoretical loss in stock price if they sell their holdings shouldn't factor in here, because it isn't universally true, and doesn't actually change the real-world value of their assets.
I too cannot liquidate my entire net worth without selling my house and car, cashing out my retirement accounts, and spending lots of fees in the process. Regardless, my net worth is still measured in the dollars those things are worth before I liquidate them, because that's how wealth is measured.
Musk spent $44B buying a website that has since plummeted in value, and his net worth has only skyrocketed since. It seems like wealth for billionaires does indeed work differently than wealth for the rest of us, and it is fact MORE forgiving for billionaires than it is for us.